The French striker has been playing through a left ankle issue for several weeks, but after further assessment the club’s medical staff have advised the player to rest and strengthen his ankle.
Unai Emery’s side face Watford this weekend, while Lacazette will also miss their opening Europa League game against Eintracht Frankfurt.
Lacazette was not required by France during the international break despite making a goal-scoring start to the new season, including getting the first as Arsenal came from behind to draw with Tottenham.
In better news for Emery, Rob Holding and Hector Bellerin are both back in training.
New signing Kieran Tierney has also trained with his new club for the first time this week.
Arsenal visit Vicarage Road on Sunday as manager Quique Sanchez Flores’ first opponents since returning to Watford.
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